Electrostatic transfer-printing sheet stripping device

ABSTRACT

A device wherein a transfer-printing sheet electrostatically adhering to the photosensitive surface of a photoreceptor after an electrostatic latent image has been formed thereon by transfer-printing from the photoreceptor is subjected to optical illumination to remove the residual charge from the photosensitive surface so as to permit the transfer-printing sheet to be easily peeled off the photoreceptor.

United States Patent 1191 Okamoto et al.

[ Nov. 26, 1974 June 9, 1972 ELECTROSTATIC TRANSFER-PRINTING SHEETSTRIPPING DEVICE Inventors: Toyoo Okamoto, Tokyo; Toshio Watanabe,Yokohama, both of Japan Assignee: Ricoh Co. Ltd., Tokyo, Japan Filed:May 18, 1973 Appl. No.: 361,646

Foreign Application Priority Data Japan 47-68643 u.s. Cl. 317/262 A,317/2 R, 355/3 1m. 0.; G03g 13/18 Field of Search 317/211, 262 A;271/51,

References Cited UNITED STATES PATENTS 4/l97l Eppe 355/3 PrimaryExaminer--J. D. Miller Assistant Examiner-Harry E. Moose, Jr.

Attorney, Agent, or FirmCooper, Dunham, Clark, Griffin & Moran [5 7]ABSTRACT A device wherein a transfer-printing sheet electrostaticallyadhering to the photosensitive surface of a photoreceptor after anelectrostatic latent image has been formed thereon by transfer-printingfrom the photoreceptor is subjected to optical illumination to removethe residual charge from the photosensitive surface so as to permit thetransfer-printing sheet to be easily peeled off the photoreceptor.

10 Claims, 3 Drawing Figures PATENTE HUVZB I974 FEG.

ELECTROSTATIC TRANSFER-PRINTING SHEET STRIPPING DEVICE BACKGROUND OF THEINVENTIOn This invention relates to electrostatic transfer printingsheet stripping devices, and more particularly to such a device adaptedfor use with electrophotographic copying apparatus of thetransfer-printing type.

In electrophotography of the transfer-printing type, a transfer-printingsheet is brought into pressing engagement with an electrophotographicphotoreceptor, such for example as a photosensitive drum orphotosensitive belt on which an electrostatic latent image is formed, toform in turn an electrostatic latent image on the transfer-printingsheet by transfer-printing from the photoreceptor. A developing agentcontaining toner particles is then supplied to the electrostatic latentimage on the transfer-printing sheet to develop it into a visible tonerimage.

Difficulty is experienced in separating the transferprinting sheet fromthe photoreceptor after they have been brought into pressing engagementwith each other to form an electrostatic latent image on thetransferprinting sheet, because the transfer-printing sheet iselectrostatically attracted to the photoreceptor on which theelectrostatic latent image is formed.

In order to obviate this problem, several attempts have been made tofacilitate stripping of the transferprinting sheet from thephotoreceptor. These include: the flowing of a stream of compressed airagainst the leading end portion of the transfer-printing sheet and thephotoreceptor; utilizing negative or subatmospheric pressure to peel offthe leading end portion of the transfer-printing sheet from thephotoreceptor; giving a push as by a lever to the leading end portion ofthe transfer-printing sheet from inside the photoreceptor in drum form;flipping up the transfer-printing sheet by means of a separatorextending through a cutout formed in the photoreceptor in drum form; andusing a photoreceptor in drum form having an axial length smaller thanthe width of the transfer-printing sheet so that the marginal portion orportions of the photoreceptor extending outwardly from the outerperiphery of the photosensitive drum may be moved upwardly as by a guideplate to peel off the transferprinting sheet from the photosensitivedrum.

These stripping means all have disadvantages. Means using compressed airis large in size and cumbersome. The use of a lever to push the leadingend portion of the transfer-printing sheet from inside thephotosensitive drum or the use of a separator extending through thecutout formed in the drum makes it necessary to increase the size of thedrum more than is necessary and complicates the construction of thedrum. In addition, problems arise as to how to operate such separatormeans with proper timing and with reliability in performance. The use ofa photosensitive drum having a smaller axial length than the width ofthe transferprinting sheet may result in the image formed on thetransfer printing sheet being defective.

SUMMARY OF THE INVENTION This invention involves an electrostatistransferprinting sheet stripping device, simple in construction and highin efficiency, in which a transfer-printing sheet electrostaticallyadhering to the photosensitive surface of a photoreceptor, after anelectrostatic latent image has been formed thereon by transfer-printingfrom the photoreceptor, is subjected to optical illumination to removethe residual charge from the photosensitive surface so as to permit thetransfer-printing sheet to be'easily peeled off from the photoreceptor.

According to the invention, there is provided a device which permits atransfer-printing sheet positively to be peeled off from a photoreceptorwithout using a bulky apparatus and complex mechanism. If thephotosensitive surface of the photoreceptor is continuously exposed tooptical illumination according to the invention, it is possible toremove the residual charge on the photosensitive drum. This is conduciveto prevention of deterioration of the photoreceptor due to dischargebreakdown.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of theelectrostatic transferprinting sheet stripping device comprising oneembodiment of this invention;

FIG. 2 is a perspective view, on an enlarged scale, of the essentialportions of the stripping device shown in FIG. 1; and

FIG. 3 is a sectional view of the electrostatic transferprinting sheetstripping device comprising another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION The invention willbe described with reference to embodiments shown in the drawings whereinthe photoreceptor is a photosensitive drum.

First, the transfer-printing operation in electrophotography wherein thephotosensitive drum moves in revolving motion will be describedfunctionally. As shown in FIG. 1, the photoreceptor of anelectrophotographic copying apparatus of the transfer-printing typecomprises an annular supporter l, and a photoconductive material layeror a photosensitive surface2 formed on the outer surface of thesupporter l which make up a photosensitive drum 3 rotating in thedirection of an arrow a so that the transfer-printing operation may beperformed continuously by the photosensitive surface 2.

The photosensitive drum 3, which is supported for rotation by a shaft 4,is rotated at a constant rate from a synchronous motor (not shown). Whenthe photosensitive drum 3 rotates, the photosensitive surface 2 isuniformly charged by a charging device 5 which is disposed in thecharging station along the path of movement of the periphery of the drum3 and comprises one or more corona discharge electrodes 7 energized by ahigh voltage power source and enclosed by shield means 6. The chargingdevice 5 extends across the width of the periphery of the drum 3. Inthis station, an electrostatic charge is uniformly applied to thephotoconductive material layer of the photosensitive drum 3.

latent image thereon. The photosensitive surface 2 of the drum 3 has apotential ranging from about 1000 volts to volts when the electrostaticlatent image is formed thereon.

The transfer-printing device is disposed next to the exposing devicealong the path of movement of the periphery of the drum 3, in thetransfer-printing position at which an electrostatic latent image isformed on a transfer-printing sheet 9 by transfer-printing from thephotosensitive surface 2 of the drum 3. That is, the electrostaticlatent image formed on the photosensitive surface of the drum istransferred to the photosensitive sheet 9 which may be made of paper orany other suitable material. The transfer-printing sheet 9 isautomatically fed by a pair of sheet feed rollers 10a and 10b andbrought into contact with the electrostatic latent image on thephotosensitive surface 2 of the drum 3. The transfer-printing sheet 9 ismaintained in contact with the electrostatic latent image and pressed atits back by a transfer-printing roller 11 so that transfer-printing ofthe electrostatic latent image may be effected.

The transfer-printing roller 1 l, which is rotated in the direction ofan arrow b by a drive mechanism (not shown) is adapted to bear againstthe transfer-printing sheet 9 when the transfer-printing is effected. Anelectrically conductive roller may be used as the transferprintingroller 11 and a bias voltage may be impressed thereon to promotetransfer-printing of the electrostatic latent image. A transfer-printingaid in the form of a transfer-printing belt may be used in place of thetransfer-printing roller 11.

The transfer-printing sheet 9 on which the electrostatic latent imagehas been formed by transfer-printing from the photosensitive surface 2of the drum 3 is then peeled off the drum 3 by the stripping deviceaccording to the invention and delivered to a developing device (notshown).

The stripping device according to the invention is disposed next to thetransfer-printing device and comprises a light source 12 and a reflector13 for directing light rays in the visible region against thetransferprinting sheet and the photosensitive surface 2 of the drum 3 onwhich the electrostatic latent image still remains.

The light source 12 comprises a cylindrical lamp as shown in FIG. 2, andis enclosed by the reflector 13 which is formed on its inner surfacewith a reflecting surface 13a. The light rays emanating from the lightsource 12 are reflected and converged by the reflector 13 as they moveupwardly and directed toward the photosensitive drum surface adjacentthe transfer-printing position. The reflector 13 is made by bending aplate into a shape which is substantially in the form of a letter U incross-section, and has an opening 13b in its upper end which is about 5millimeters in width.

The reflector 13 is disposed such that its upper opening 13b is inspaced juxtaposed relationship to the back of the transfer-printingsheet 9 which has been brought into pressing engagement with thephotosensitive surface 2 of the drum 3. One of two edges forming theupper opening 13b which is disposed remote from the transfer-printingroller 11 has an extension 13c which is disposed horizontally to serveas a guide for delivering the transfer-printing sheet 9 to thedeveloping device after transfer-printing is effected. A guide plate 14is disposed in spaced juxtaposed relationship to the extension 13c todefine therebetween a transfer-printing sheet passage. I 1

In operation, light rays for stripping the transferprinting sheet 9 aredirected against the leading end portion of the transfer-printing sheetafter transfer-printing is effected. More specifically, if the lightsource 12 is turned on when it is desired to perform a strippingoperation, the light rays emanating therefrom will be reflected by thereflector l3 and radiated through the opening 13b. The transfer-printingsheet 9 and the photosensitive surface 2 of the drum 3 are exposed tothe light rays, so that the residual charge on the photosensitivesurface 2 is removed. The transfer-printing efficiency is about 1/10when the electrostatic latent image formed on the photosensitive surface2 of the drum 3 is transferred to the transfer-printing sheet by thepressure applied by the transfer-printing roller 11. Thus more or lesselectrostatic charge remains on the photosensitive surface 2 of the drum3 after transfer-printing is effected, and the transfer-printing sheet 9sticks to the photosensitive surface 2 by electrostatic adhesion.

However, by exposing the transfer-printing sheet and the photosensitivesurface of the drum to light rays as aforementioned, it is possible toremove the residual charge from the photosensitive surface and peel offthe transfer-printing sheet from the photosensitive surface of the drumso that the transfer-printing sheet may move in its travel toward thedeveloping device.

Since the transfer-printing sheet 9 is made of an insulator, the chargecarried thereon is not removed even if it is exposed to light rays.

From the foregoing description, it will be appreciated that thetransfer-printing sheet adhering to the photosensitive surface of thedrum can be readily and positively peeled off therefrom. Thetransfer-printing sheet released from engagement with the drum isdelivered by a pair of conveyor rollers 15a and 15b to the developingdevice.

The opening 13b of the reflector 13 is narrowed in order to make thelight rays converge and to prevent the leading end of the strippedtransfer-printing sheet from finding its way through the opening 13binto the reflector 13. When the opening 13b is increased in width,strings or wires may be trained in the opening 13b in the direction ofmovement of the transferprinting sheet.

FIG. 3 shows another embodiment in which light rays of high intensityare directed to the stripping position. In this embodiment, a reflector23 has a reflecting surface 23a of the shape whhich corresponds toone-half portion of an ellipse cut along its major axis. The lgihtsource 12 is arranged such that it is disposed in a first focusingposition of the reflector 23, and a second focusing position of thereflector 23 corresponds to the stripping position at the leading endportion of the transfer-printing sheet 9. By this arrangement, lightrays reflected by the reflector 23 converge at the second focusingposition of the reflector 23 so that stripping light of high intensitycan be directed to the stripping position.

When it is desired to illuminate the stripping position with parallellight rays, a parabolic mirror may be used as the reflector 23.

From the foregoing description, it will be appreciated that thestripping device according to the invention readily permits thetransfer-printing sheet to be peeled off from the photosensitive surfaceof the photosensitive drum after an electrostatic latent image is formedon the transfer-printing sheet by transfer printing from thephotosensitive surface through illuminating the back of thetransfer-printing sheet by throwing optical light on to the strippingposition near the transferprinting position in which thetransfer-printing sheet is brought into pressing engagement with thephotosensitive surface of the drum.

If the transfer-printing sheet 9 is a sheet of paper having its surfacetreated with a dielectric material, the device according to theinvention can achieve better results.

What is claimed is:

1. An electrostatic transfer-printing device of the type comprising:

a. a photoreceptor having a photosensitive surface on which anelectrostatic latent image is formed for transfer to a transfer-printingsheet;

wherein the improvement comprises:

b. means for bringing one surface of a transferprinting sheet intopressing engagement with the photosensitive surface at atransfer-printing position and for applying a voltage to the othersurface of said sheet, of opposite polarity from that of theelectrostatic latent image charge, to transfer said image onto saidtransfer-printing sheet by transferprinting from the photosensitivesurface; and g c. illumination means for throwing visible light raysonto the photosenitive surface adjacent the transfer-printing positionafter the transfer-printing sheet is brought into pressing contact withthe photosensitive surface of the photoreceptor to illuminate thetransfer-printing sheet on which the electrostatic latent image has beenformed and the photosensitive surface of the photoreceptor on whichthere is a residual charge so as to remove said residual chargesufficiently to release said transferprinting sheet from saidphotosensitive surface.

2. A device as in claim 1 wherein said illumination means comprises alight source and a reflector for directing said light rays onto saidphotosensitive surface.

3. A device as in claim 2 wherein said reflector has a reflectingsurface of the shape which corresponds to onehalf portion of an ellipsecut along its major axis.

4. A device as in claim 3 wherein the edge of said reflector remote fromthe transfer-printing position has an extension thereon for guiding saidtransfer-printing sheet after release.

5. A device as in claim 1 including guide means for guiding saidtransfer printing sheet after illumination by said illuminating means.

6. A method for stripping a transfer-printing sheet from thephotosensitive surface of a photoreceptor against which it has beenpressed to transfer-print a latent electrostatic image on one surfacethereof comprising the steps of applying a voltage of opposite polarityto that of the latent electrostatic image charge to the other surface ofsaid sheet during the pressing and shining visible light rays onto thephotosensitive surface of said photoreceptor adjacent thetransfer-printing position after the transfer printing to illuminate thetransfer-printing sheet on which the electrostatic latent image has beenformed and the photosensitive surface of the photoreceptor on whichthere is a residual charge so as to remove said residual chargesufficiently to release said transfer-printing sheet from saidphotosensitive surface.

7. A method as in claim 6 wherein said light rays are I shone by meansof a light source and further comprising the step of disposing areflector about said light source for directing and concentrating saidlight rays onto said photosensitive surface.

8. A method as in claim 7 wherein saidreflector is formed by the step ofbending a flat plate into a shape which is substantially in the form ofa letter u in cross section and has a narrowed upper opening.

9. A method as in claim 6 wherein the transfer printing sheet is made ofpaper and its surface is treated with a dielectric material.

10. A method as in claim 6 including the step of providing a guide wayfor the transfer printing sheet after shining the light rays thereon.

1. An electrostatic transfer-printing device of the type comprising: a.a photoreceptor having a photosensitive surface on which anelectrostatic latent image is formed for transfer to a transfer-printingsheet; wherein the improvement comprises: b. means for bringing onesurface of a transfer-printing sheet into pressing engagement with thephotosensitive surface at a transfer-printing position and for applyinga voltage to the other surface of said sheet, of opposite polarity fromthat of the electrostatic latent image charge, to transfer said imageonto said transfer-printing sheet by transfer-printing from thephotosensitive surface; and c. illumination means for throwing visiblelight rays onto the photosenitive surface adjacent the transfer-printingposition after the transfer-printing sheet is brought into pressingcontact with the photosensitive surface of the photoreceptor toilluminate the transfer-printing sheet on which the electrostatic latentimage hAs been formed and the photosensitive surface of thephotoreceptor on which there is a residual charge so as to remove saidresidual charge sufficiently to release said transfer-printing sheetfrom said photosensitive surface.
 2. A device as in claim 1 wherein saidillumination means comprises a light source and a reflector fordirecting said light rays onto said photosensitive surface.
 3. A deviceas in claim 2 wherein said reflector has a reflecting surface of theshape which corresponds to one-half portion of an ellipse cut along itsmajor axis.
 4. A device as in claim 3 wherein the edge of said reflectorremote from the transfer-printing position has an extension thereon forguiding said transfer-printing sheet after release.
 5. A device as inclaim 1 including guide means for guiding said transfer printing sheetafter illumination by said illuminating means.
 6. A method for strippinga transfer-printing sheet from the photosensitive surface of aphotoreceptor against which it has been pressed to transfer-print alatent electrostatic image on one surface thereof comprising the stepsof applying a voltage of opposite polarity to that of the latentelectrostatic image charge to the other surface of said sheet during thepressing and shining visible light rays onto the photosensitive surfaceof said photoreceptor adjacent the transfer-printing position after thetransfer printing to illuminate the transfer-printing sheet on which theelectrostatic latent image has been formed and the photosensitivesurface of the photoreceptor on which there is a residual charge so asto remove said residual charge sufficiently to release saidtransfer-printing sheet from said photosensitive surface.
 7. A method asin claim 6 wherein said light rays are shone by means of a light sourceand further comprising the step of disposing a reflector about saidlight source for directing and concentrating said light rays onto saidphotosensitive surface.
 8. A method as in claim 7 wherein said reflectoris formed by the step of bending a flat plate into a shape which issubstantially in the form of a letter u in cross section and has anarrowed upper opening.
 9. A method as in claim 6 wherein the transferprinting sheet is made of paper and its surface is treated with adielectric material.
 10. A method as in claim 6 including the step ofproviding a guide way for the transfer printing sheet after shining thelight rays thereon.